U.S. mayors to back gay marriage this week

Mayors of some of the largest cities in the U.S. are expected to announce an organized effort in support of gay marriage at the U.S. Conference of Mayors annual gathering this weekend in Washington, D.C.

Chicago Mayor Rahm Emanuel (pictured), New York City Michael Bloomberg, Los Angeles Mayor Antonio Villaraigosa, Houston Mayor Annise Parker, and Joe Sanders, the Republican mayor of San Diego are among the 70 city leaders joining the group Mayors for the Freedom to Marry.

The group is backed by the national marriage equality group Freedom to Marry and said in a joint statement: 'By joining the group, mayors hope to expand public and political support for ending the exclusion of same-sex couples from marriage.'

Mayors for the Freedom to Marry will be co-chaired by Sanders, Villariagosa and Boston Mayor Thomas Menino.

Sanders pro-gay marriage is a rare when it comes to high-profile Republican elected officials. The San Diego mayor was once against marriage equality but in 2007, he announced a change of heart.

At an emotional press conference that year he said: 'I have close family members and friends who are members of the gay and lesbian community. Those folks include my daughter Lisa.'

The effort by the mayors comes as Republican presidential hopefuls including Mitt Romney, Rick Santorum and Rick Perry speak out against gay marriage and for a federal law not recognizing them even if they take place in states where such unions are legal.

President Barack Obama has not come out in favor of gay marriage although he did instruct the Justice Department last year to stop defending the Defense of Marriage Act (DOMA), the legal prohibition on federal recognition of same-sex marriages.